Agriculture Reference
In-Depth Information
except FIT, which is solely induced in roots [38]. To our knowledge, no
homologs of these bHLH TFs have been identified in pea yet.
The regulation of the morphological Fe responses by Strategy I plants is
not totally known but there is evidence suggesting that the plant hormones
ethylene, auxin and NO are involved in their activation [14,46-47]. In relation
to the regulation of the physiological Fe responses, in the last years
physiological and molecular evidence has been accumulating suggesting a key
role for the plant hormone ethylene (in conjunction with other hormones, such
as auxin and NO) as activator of the expression of the master regulator FER
(and FIT) and, consequently, of most of the Fe acquisition genes, while some
signal related to phloem Fe would act to repress their expression [34-35,48-
49]. In a very recent review [35], a model for the regulation of physiological
Fe responses in dicots has been proposed, that integrate both positive signals
(such as ethylene, auxin, and NO) and negative signals (such as Fe coming
from shoots to roots through the phloem).
In the study of the regulation of Fe responses by Strategy I plants, it has
been very important the use of mutants with altered regulation of these
responses, such as the pea
brz
and
dgl
mutants (see Use of mutants…).
U
SE OF
M
UTANTS TO
S
TUDY
R
EGULATION
:
P
EA
BRZ
AND
DGL
Despite the involvement of ethylene and phloem Fe in the regulation of
physiological Fe responses by Strategy I plants, there are still many questions
to solve. As examples, it is necessary to clarify which is exactly the Fe-related
compound moving in the phloem that acts as repressive signal of Fe responses
in roots. Additionally, it is also necessary to know how interacts this Fe-related
compound with ethylene (and other hormones, such as NO) in the roots.
For the study of the regulation of Fe responses, the use of mutants has
been, and will be, fundamental. We can classify the mutants employed in two
main categories: hormonal mutants and mutants altered in the regulation of Fe
responses. Hormonal mutants are mutants altered in the production or perception
of a particular hormone, and have been used to analyze the participation of
hormones in the regulation of Fe responses. During the last years, Fe researchers
have used mutants related to several hormones but most of the works have been
done with ethylene mutants: ethylene insensitive mutants (Arabidopsis
etr1
,
ein2
and
ein3eil1
,…;
Medicago truncatula
sickle
; Soybean
etr1
), ethylene constitutive
